Form-fill-and-seal machines are commonly used to package many items, such as snack foods, candies and the like, in flexible bags. These machines utilize a continuous roll of packaging material to form a bag, fill the bag with product, and seal the bag. Continuity and completeness of the sealing function, both back and end seals, is of crucial importance to packaging snack foods, as a leak in the bag can lead to loss of product freshness. To this end, much effort has been devoted to the development of apparatus to produce back and end seals with a high degree of integrity. One such back seal that has been developed is a fin-type seal wherein the inner sealable face of one edge portion of the packaging material makes with the inner sealable face of the opposite edge portion which is folded together in one direction back towards the so-formed bag. Sealing means is applied so that the two mated edges form a fin-type seal.
Various problems are inherent to fin-type back seals. A prevalent problem is adherence of the sealing material to the processing equipment. Especially with thermally sealed packaging materials, undesirable adherence to the process equipment can cause incomplete seals, torn packaging material and unwanted machine downtime. Poorly mated edge seals can also display the inner sealing layer which is frequently not the same color as the exterior of the package. This detracts from the overall appearance of the finished product. A final concern with forming fin-type seals is the tendency toward arcuate misalignment along the fin length which sometimes fails to form a continuous seal. This inherent preference for arcuate misalignment is especially pronounced when the packaging material is an all polymeric material such as multi-plies of polypropylene and polyethylene.
U.S. Pat. No. 3,935,048 to Rucker entitled "Method for Forming Containers With Fin-Type Seams" addressed the problems inherent in forming fin-type seals. Rucker disclosed an apparatus wherein the mated edges of the packaging film are pulled and slid over a backup plate extending between the mated edges and the body of the packaging material to prevent scuffing of the heat sealable material against a back supporting filling tube. A tracking wheel engaging the mated edges presses them against the backup plate to maintain alignment. While this teaching addressed several of the problems inherent with fin-type seals using end seal jaw advancement of the film, problems still remain with fin-type seals, such as arcuate misalignment on machines where the film is advanced by side pull belts and sealed later. What is needed is an improved apparatus for providing uniform fin-type back seals of flexible packaging material.
It is one object of the present invention to provide an apparatus for producing uniform fin-type back seals of flexible packaging material in conjunction with form-fill-and-seal machines.
It is a second object of the present invention to provide a method by which such uniform fin-type seals may be obtained.
These and other objects of the present invention will become obvious from the following description of the invention and the appended claims.